Bovine hard cheeses such as Asiago, Parmesan, and Romano are widely sold and consumed in pre-grated form for convenience, and any adulteration is difficult to detect visually. In this study, an analytical method was developed using a simple organic extraction to verify the authenticity of bovine hard cheese products by examining the lipid profile of these cheeses using proton Nuclear Magnetic Resonance (NMR) spectroscopy. Sample preparation by the extraction of lipid material from the cheese was achieved using deuterated chloroform ( (CDCl3 99.8% D), which avoided the time consuming preparation of derivatisation for gas chromatography of non-volatile compounds, hydrolysis of triacylglycerols for analysis of lipids in mass spectrometry. Ungrated samples of the hard cheese (Parmesan, Romano and Asiago) were analysed by proton NMR to ascertain a lipid profile of unadulterated cheese samples. A series of adulterated samples were prepared with vegetable oil adulteration in ranges from 5–60 weight% using rapeseed, grapeseed, peanut, olive, high oleic sunflower, high oleic safflower, high linolenic safflower, soybean, and palm oils, and lipid profiles of these were determined by NMR. The ungrated cheeses were found to have a very consistent lipid profile from sample to sample, improving the power of this approach to detect vegetable oil adulteration.However, it also revealed that the palm oil adulterated samples yielded a lipid profile nearly identical to one of the authentic cheese samples. Quantification of the level of palm oil adulteration in these samples was achieved by generating calibration curves of two peak ratios.
In order to test out the method, 52 market samples of grated Parmesan, Romano, and Asiago cheese were purchased from retailers, restaurants, and public school cafeteria kitchens and analysed by NMR. It was found that 29% of all samples tested were certainly adulterated with palm oil. Palm oil is a clever adulterant owing to its similar lipid profile. Also, it is semi-solid at room temperature with a similar colour to cheese, and a low price compared to cheese.
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